For factory ammo to keyhole, it's usually a problem with the rifle and not the ammo.
First thing to check is that the ammo is the same caliber that's marked on the barrel. For instance a 30-30 round fired in a .32 special rifle.
The next thing to check is the condition of the bore, especially at the muzzle. Is it clean and free of corrosion, pitting? Is the muzzle damaged, dented, where the bullet emerges? If so, the escaping gases behind the bullet could be causing it to tip as it leaves the muzzle.
If the barrel bore is clean and in reasonably good condition, might there be a dent inside the bore where a front sight ramp screw hold might have been drilled a bit too deeply at the factory and the barrel steel is pressed into it? (Sounds weird, but exactly what happened to my friend's .35 Rem, Marlin 336.)
If none of the above seems to be the problem, we'll need more specific information about the rifle and the ammo used.